Biological testing has become an important tool in detecting and monitoring diseases. In the biological testing field, thermal cycling is used to amplify nucleic acids by, for example, performing PCR and other reactions. PCR in particular has become a valuable research tool with applications such as cloning, analysis of genetic expression, DNA sequencing, and drug discovery.
Recent developments in the field have spurred growth in the number of tests that are performed. One method for increasing the throughput of such biological testing is to provide real-time detection capability during thermal cycling. Real-time detection increases the efficiency of the biological testing because the characteristics of the samples can be detected while the sample well tray remains positioned in the thermal cycling device.
In a real-time detection system, testing may be performed on multiple samples during a cycle of the testing device. With this type of system, light may be emitted from a light source to be reflected off of the biological sample(s) and ultimately may be detected or collected by a light detecting device such as a camera or CCD, for example. To assist with focusing the light into and directing the light out of the samples toward detecting device, one or more lenses may be provided.
One of the drawbacks of conventional devices utilizing lens assemblies in conjunction with multiple sample testing devices is the complexity of the lens(es). It may often be desirable to have a lens for collimating light so that it may be properly aligned with a row or column of sample wells in a sample well tray. To further enhance the testing process, an additional lens assembly may be provided for focusing light more precisely within each of the sample wells. These focusing lens assemblies often may comprise a plurality of non-integral components, resulting in a bulky structure.
Another drawback of conventional devices is chromatic aberration. Some conventional instruments comprise light sources emitting light having one or more excitation wavelengths and samples emitting light at one or more emission wavelengths. Optical systems direct excitation light from sources to samples and/or from samples to detectors. When these systems are not corrected for chromatic aberration, vignetting and system throughput become functions of wavelength. When the systems are corrected for chromatic aberration, wavelength-dependent response variations may be substantially reduced.
Some conventional sample testing devices utilize two or more bonded lens elements that serve to collect and focus light. Such devices may have a less bulky structure, but the use of bonded elements of materials with different dispersions may result in spherical and/or chromatic aberration of the light. Some conventional refractive achromats may correct both spherical and chromatic aberrations, but typically require the use of glass and more costly fabrication.
Accordingly, it may be desirable to provide a sample testing device having a diffractive/refractive hybrid lens that reduces spherical and/or chromatic aberration of light. It may be desirable to manufacture the diffractive/refractive hybrid from a polymer with a single-step process, thus saving material and manufacturing costs.